The addition of the NX bit to CPUs blurs the line between Von Neuman and Harvard architectures. Giving an attacker a JIT makes it easier for them to lay out me

The addition of the NX bit to CPUs blurs the line between Von Neuman and Harvard architectures. Giving an attacker a JIT makes it easier for them to lay out memory with the NX bit set to zero (executable memory) that they can later jump into. Return-oriented programming can still be used to hijack a program that whose executable parts are locked down at runtime, having a JIT just makes things easier.